1. Field of the Invention
The present invention relates to improvements to a wheel support rolling bearing unit with seal ring for supporting the wheel of an automobile on a suspension device. To be specific, it realizes a structure in which, in the case where one or more seal lips are assembled in the opposite state from the correct direction (misassembled), the fact can be identified easily.
2. Description of Related Art
Heretofore, as is disclosed in Patent Documents 1 to 6 for example, a range of structures is known for a wheel support rolling bearing unit with seal ring for rotatably supporting the wheel of an automobile on a suspension device. FIG. 2 shows one example of a conventionally-known structure, which is disclosed in Patent Document 2. The wheel support rolling bearing unit with seal ring comprises an outer ring 1, a hub 2, a plurality of rolling elements 3, a seal ring 4, and a cap 5. The outer ring 1 has an external flange shaped attachment portion 6 on its outer peripheral surface for supporting and fixing the outer ring 1 on the suspension device, and a double row of outer ring raceways 7 on its inner peripheral surface. Furthermore, the hub 2 is formed by a hub body 8 and an inner ring 9, joined together, and fastened by a nut 10. A flange 11 for supporting and fixing a wheel is provided on a portion towards the axial outside end of the outer peripheral surface of the hub 2, which is the portion protruding from the outer ring 1 outwardly in the axial direction, and a double row of inner ring raceways 12 are provided on portions in the center and towards the axial inside end. (The outside relative to the axial direction means the outer side in the widthwise direction when assembled on an automobile, which is the left side in the figures. Conversely, the inside relative to the axial direction means the side towards the center in the widthwise direction, which is the right side of the figures. This terminology is also used in the present specification and the claims as a whole.) In recent years, a structure has also been widely known and implemented in which the hub body and inner rings are combined by a crimped portion, which is formed by plastically deforming radially outwards a cylindrical portion formed on the axial inside end portion of the hub body. In either case, a plurality of pieces of the abovementioned rolling elements 3 are provided for each of the two rows between the two outer ring raceways 7 and the two inner ring raceways 12 in a state where they are retained by respective cages 13. In the example in the figure, balls are used as the rolling elements 3. However, in the case of a wheel support rolling bearing unit with seal ring for heavier automobiles, tapered rollers may be used as the rolling elements.
Furthermore, the seal ring 4 is provided between the inner peripheral surface of the outer end of the outer ring 1 and the outer peripheral surface of the intermediate part of the hub 2, and it closes the outside opening of an inner space 14, which is between the inner peripheral surface of the outer ring 1 and the outer peripheral surface of the hub 2, in which the rolling elements 3 are provided. Moreover, the cap 5 closes the inside opening of the outer ring 1. By means of the cap 5 and the seal ring 4, foreign substances such as dust, rain water and the like are prevented from entering the inner space 14, and grease in the inner space 14 is prevented from leaking to the exterior.
In order to sufficiently prevent foreign substances from entering the inner space 14, and grease filling up the inner space 14 from leaking out, it is necessary to ensure the sealing performance of the seal ring 4. For a seal ring considered for this purpose, Patent Document 1 discloses a seal ring 4a as shown in FIG. 3, and Patent Document 2 discloses a seal ring 4b as shown in FIG. 4. The seal rings 4a and 4b are formed by annular shaped metal cores 15a and 15b and annular seal members 16a and 16b, respectively. Here, the metal cores 15a and 15b are made from metal plates, and are internally fixed to the outside end of the outer ring 1. Furthermore, the seal members 16a and 16b are made of an elastic material such as an elastomer including rubber or the like, and are fastened to the metal cores 15a and 15b by baking or the like. Moreover, each of the seal members 16a and 16b has three seal lips, 17a, 18a and 19a, or 17b, 18b and 19b. The seal lips 17a, 18a, 17b and 18b among the seal lips 17a, 18a, 19a, 17b, 18b and 19b, which are on the farthest side (outside) from the inner space 14, and the middle, incline outwards in the radial direction towards their tips. Each of the tips makes a sliding contact all around the circumference of the axial inside surface of the flange 11, or a curved surface portion 20, which is located on the continuous portion between the axial inside surface of the flange 11 and the outer peripheral surface of the hub 2. Moreover, the seal lips 19a and 19b on the closest side (inside) to the inner space 14 incline inwards in the axial direction towards the internal edge, being their tips, and these tips make a sliding contact all around the circumference of a cylindrical outer peripheral surface (cylindrical surface 21) located on the axial intermediate portion of the hub 2.
Among the seal lips 17a, 18a, 19a, 17b, 18b and 19b provided in the seal rings 4a and 4b as described above, the seal lips 17a, 18a, 17b and 18b on the outside and in the middle mainly contribute to preventing foreign substances from entering the inner space 14 from the outer space. Conversely, the seal lips 19a and 19b on the inside mainly contribute to preventing grease in the inner space 14 from leaking outside. Since the wheel support rolling bearing unit with seal ring shown in FIG. 2 has a structure for undriven wheels (front wheels of an FR vehicle or an MR vehicle, rear wheels of an FF vehicle), the inside opening of the outer ring 1 is closed by the cap 5. Conversely, in the case of a wheel support rolling bearing unit with seal ring for driving wheels (rear wheels of an FR vehicle or an MR vehicle, front wheels of an FF vehicle, all wheels of a 4WD vehicle), the inside opening of the inner space is closed by a seal ring such as a combinational seal ring or the like.
Whichever wheel support rolling bearing unit with seal ring for undriven wheels or driving wheels is used, the outside opening of the inner space 14 is usually closed by seal rings 4a and 4b, which are provided with three seal lips 17a, 18a and 19a, or 17b, 18b and 19b. In such seal rings 4a and 4b, in the case where the middle seal lips 18a and 18b make sliding contact with the axial inside surface of the flange 11 or the curved surface portion 20 as shown in FIGS. 3 and 4, it is not always a favorable structure from the aspect of ensuring sealing performance. That is, the axial inside surface and the curved surface portion 20 are likely to be displaced by the moment applied to the hub 2 from the wheels during traveling. In the case where they are displaced, the adherence between the tips of the middle seal lips 18a and 18b and the axial inside surface or the curved surface portion 20 deteriorates, and thus the sealing performance of the seal lips 18a and 18b is lowered. In the case where such a circumstance is considered, as in the structures disclosed in Patent Documents 5 and 6, it is also desirable for the middle seal lips to make sliding contact with the cylindrical outer peripheral surface located on the axial intermediate portion of the hub 2.
FIG. 5 shows a seal ring 4c in which such a circumstance is considered. Among three seal lips 17c, 18c and 19c of a seal member 16c constituting the seal ring 4c together with a metal core 15c, the seal lip 17c on the outside and the seal lip 19c on the inside make sliding contact all around the circumference of the axial inside surface of the flange 11 and the cylindrical surface 21 located on the outer peripheral surface of the axial intermediate portion of the hub 2, respectively, similarly to the structures shown in FIGS. 3 and 4. In particular, in the case of the structure shown in FIG. 5, the middle seal lip 18c is inclined in a direction outwards in the axial direction towards the internal edge, being its tip, and this tip makes a sliding contact all around the circumference of the cylindrical surface 21. In the case of the structure shown in FIG. 5 also, similarly to the structures shown in FIGS. 3 and 4, the seal lips 17c and 18c on the outside and in the middle mainly contribute to preventing foreign substances from entering the inner space 14 from the outer space, and the seal lip 19c on the inner side mainly contributes to preventing grease in the inner space 14 from leaking out. The sliding contact condition between the tips of the seal lips 18c and 19c, in the middle and on the inside, and the cylindrical surface 21 can be made stable regardless of the moment applied to the hub 2 during traveling. Therefore, the structure shown in FIG. 5 enables the performance of preventing foreign substances from entering the inner space 14 to be improved in comparison with the structures shown in FIGS. 3 and 4.
However, in the case of the structure shown in FIG. 5, there is a possibility that the following problem occurs due to the shape of the middle seal lip 18c. That is, since it is necessary for the tip of the seal lip 18c to make contact with the cylindrical surface 21 in a state in which the required contact pressure is ensured all around the circumference, the inner diameter of the seal lip 18c in a free state is slightly smaller than the diameter (outer diameter) of the cylindrical surface 21. When assembling the wheel support rolling bearing unit with seal ring, the seal ring 4c, which has been internally secured to the axial outside end of the outer ring 1 in advance, is fitted onto the intermediate portion of the hub 2. At this time, the internal edge of the middle seal lip 18c is guided by a sloping guide surface 22 provided between the axial outside inner ring raceway 12 provided on the outer peripheral surface of the intermediate portion of the hub 2, and the cylindrical surface 21, and slips onto the cylindrical surface 21 while its inner diameter is expanded elastically.
The assembly operation of the wheel support rolling bearing unit with seal ring as described above is performed with the outer ring 1 and the hub 2 aligned. However, if the central axes of the two members 1 and 2 are shifted even slightly for some reason, the overlap of the middle seal lip 18c and the guide inclined surface 22 becomes too large. In this case, as shown by the chain lines in FIG. 5, there is a possibility of the seal lip 18c being assembled while being elastically deformed (turned back) inwards in the axial direction towards its tip, which is the opposite of the correct state. In the case where the middle seal lip 18c is assembled reversed in this manner, not only does the sealing performance by the seal lip 18c deteriorate, but also the friction between the tip of the seal lip 18c and the cylindrical surface 21 increases, and hence the dynamic torque of the wheel support rolling bearing unit with seal ring increases. The deterioration of the sealing performance becomes the cause of a drop in the durability of the wheel support rolling bearing unit with seal ring due to foreign substances entering the inner space 14. Furthermore, the increase in the dynamic torque becomes the cause of a drop in acceleration and fuel consumption performance due to the increase in the resistance against the rotation of the wheel.
If misassembly of the middle seal lip 18c, which is the cause of such a failure occurring, can be identified easily, it is possible to prevent the failure occurring by disassembling and reassembling the concerned rolling bearing unit with seal ring. However, the middle seal lip 18c cannot be observed visually from outside after the rolling bearing unit with seal ring is assembled. Moreover, since the increase of the dynamic torque is small, it is difficult to detect the misassembly by measuring the dynamic torque.
[Patent Document 1] Japanese Utility Model Application Publication No. H7-34224
[Patent Document 2] Japanese Patent Application Publication No. H9-287619
[Patent Document 3] Japanese Patent Application Publication No. H11-210770
[Patent Document 4] Japanese Patent Application Publication No. 2003-56577
[Patent Document 5] Japanese Patent Application Publication No. 2004-204894
[Patent Document 6] Japanese Patent Application Publication No. 2004-205277